Acoustic coupling with a fluid bath

ABSTRACT

An apparatus examines the internal structure of an object disposed substantially in a medium such as air, which essentially totally reflects acoustic signals in the 1-200 MHz frequency range. The apparatus has an acoustic transducer that emits and receives acoustic signals in the 1-200 MHz frequency range and an acoustic coupler that acoustically couples the acoustic transducer to the object. The acoustic coupler is adapted to essentially retain a body of fluid such as water between a section of the surface of the object and the acoustic transducer for carrying acoustic signals in the 1-200 MHz frequency range between the acoustic transducer and the object.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to co-pending U.S. provisionalapplications entitled: “Scanning Acoustic Microscopy,” having ser. no.60/355,201, filed Feb. 8, 2002; which is entirely incorporated byreference; “Acoustic Coupling,” having ser. no. 60/355,649, filed Feb.8, 2002; which is entirely incorporated by reference; and “Apparatus ForReflection Mode Acoustic Microscopy Scanning Of An Object,” having Ser.No. 60/378,540, filed May 7, 2002. This application is one of fiveco-pending, commonly assigned U.S. Patent Applications all of which havethe same filing date of May 31, 2002. The other co-pending Applicationsare entitled “Flowing Fluid Acoustic Coupling,” Ser. No. 10/159,585;“Scanning Acoustic Microscopy,” Ser. No. 10/159,547; “Acoustic CouplingWith A Fluid Retainer,” Ser. No. 10/159,441; and “Non-Fluid AcousticCoupling,” Ser. No. 10/191,044, and all of the above-mentionedco-pending applications are hereby incorporated into this document byreference.

TECHNICAL FIELD

The present invention is generally related to the examining of theinternal structure of materials and, more particularly, is related to asystem and method for the non-destructive internal examination of amaterial.

BACKGROUND OF THE INVENTION

If a structure, such as a machine or a part of a product, has a defect,such as a crack, a void, or a recess, there is a risk that the machineor part will become inoperable due to the defect. Thus, it is desiredthat the part having such a defect is eliminated or replaced bydetecting the presence of such a defect in advance of the machine orpart becoming inoperable. For example, aircraft skins and othermanufactured components are frequently made from laminates, which arelayers of material adhered together by layers of adhesive, such as, butnot limited to, sealant, epoxy, and glue, interposing the layers ofmaterial. Laminates can delaminate when the adhesive layers can nolonger adhere the layers of material together. Typically, delaminationdoes not occur spontaneously, but rather, it occurs after voids haveformed in the adhesive layers. In addition to concerns aboutdelamination due to voids, laminates can also fail due to cracks. Thus,it is desirable to examine by non-destructive means the internalstructure of a laminate to search for voids, cracks, and other internaldefects before the laminate fails.

It is desirable that the examination of an object occurs in situ. Insitu examination of a component can typically be done more rapidly andinexpensively than non-in situ because there it requires lessdisassembly and reassembly of the system. It is also desirable that theapparatus used for examining the component be readily transportable.

Thus, a heretofore-unaddressed need exists in the industry to addressthe aforementioned deficiencies and inadequacies.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the invention can be better understood with reference tothe following drawings. The components in the drawings are notnecessarily to scale, emphasis instead being placed upon clearlyillustrating the principles of the present invention. Moreover, in thedrawings, like reference numerals designate corresponding partsthroughout the several views.

FIG. 1 is a perspective view of a moveable acoustic scanning systemscanning a section of an aircraft.

FIG. 2A is a perspective view of an acoustic scanning apparatus attachedto a section of an aircraft.

FIG. 2B is a perspective view of an acoustic transducer pivotingassembly.

FIG. 3 is top view of an acoustic scanning apparatus attached to asection of an aircraft.

FIG. 4 is diagram of an acoustic transducer assembly emitting anacoustic signal onto a laminate and the reflected acoustic signals.

FIG. 5 is a graph of reflected acoustic signals received by an acoustictransducer versus time.

FIG. 6 is a two dimensional image of the internal structure of a layerof an object.

FIG. 7 is block diagram of a computer.

FIG. 8 is a block diagram of a controller.

FIG. 9 is a is a flow chart of one example method for scanning asurface.

FIG. 10 is a side view of an acoustic transducer pivoting assembly andan acoustic transducer assembly-solid acoustic coupler.

FIG. 11 is perspective view of an acoustical acoustic transducerassembly sprayer.

FIG. 12 is a side view of an acoustic transducer assembly-fluidretainer.

FIG. 13 is cut away view of a fluid bath acoustic coupler.

DETAILED DESCRIPTION

Referring to FIG. 1, a moveable acoustic scanning system (MASS) 10 isused to scan the skin 6 of an aircraft 8. The MASS 10 includes anacoustic scanning assembly (ASA) 14 attached to a positioning apparatus12. The positioning apparatus 12 includes a base 20 and an extendablearm 18 that extends from base 20. The positioning apparatus includes acontrol system 16, which is typically a computer, or the like, that isused for, among other things, controlling arm 18. In one preferredembodiment, the base 20 is moveable so that the arm 18 can be readilymoved around the aircraft 8 and positioned near subsequent aircraft.Non-limiting examples of a moveable base include but are not limited totrucks, trolleys, carts, scissor-jack, sky-jacks, and hand cars. Withthe arm 18 positioned proximal to the aircraft 8, the arm 18 is used toposition the ASA 14 proximal to selected portions of the aircraft 8. Inone preferred embodiment, the arm 18 is adapted to move inthree-dimensions so that the ASA 14 can be positioned against theaircraft 8 in orientations ranging from horizontal to vertical. In onepreferred embodiment, the arm 18 includes a mechanism such as, but notlimited to, hydraulically actuated jaws or clamps (not shown) that gripthe ASA 14. After the ASA 14 is attached to the skin 6 of the aircraft8, the control system 16 releases the ASA 14 so that they are notrigidly coupled together during a scan. The arm 18 releases the ASA 14so that vibrations are not transmitted from the arm 18 to the ASA 14. Inanother embodiment, the ASA 14 is manually positioned against selectedportions of the aircraft 8.

In one preferred embodiment, the ASA 14 is used to scan a section of theaircraft 8, and when the scan of that section is completed, thecontroller 16 repositions the ASA 14 to a new section of the aircraft 8.In this manner, the entire skin 6 of the aircraft 8 may be scanned, orselected sections of the aircraft are scanned. The ASA 14 is adapted toscan sections of the aircraft 8 that range in size of up toapproximately one meter in length and up to approximately one meter inwidth. The ASA 14 can be used to scan a portion of the aircraft 8 thatis larger than one meter in length by simply scanning that portion ofthe aircraft 8 in segments. In other embodiments, the ASA 14 is adaptedto scan sections that are either longer or wider or both than one meter.

Typically, the ASA 14 is positioned on the aircraft 8 by the controller16 manipulating the arm 18. However, in one embodiment, the operatormanually controls the arm 18 using controls (not shown) for positioningthe ASA 14 against the aircraft 8. Typically, the ASA 14 is positionedagainst the aircraft 8 within a tolerance of a couple of inches from thedesired location, and the ASA 14 can resolve features in the 1 to 200micron range. A relatively precise determination of the location of theASA 14 is determined by comparing the scanned structural features suchas rivets with their known locations. Thus, although it is preferable toposition the ASA 14 as close as possible to a desired location so as toreduce the amount of unnecessary scanning, it is not necessary to placeit in an exact location because a precise position of the ASA 14 isdetermined from the scanning results. Therefore, it is not necessary forthe operator to spend an inordinate amount of time positioning the ASA14 to an exact location.

Acoustic Scanning Assembly

Referring now to FIG. 2, the ASA 14 includes a base-frame 22, a moveableplatform 24, and an acoustic transducer pivoting assembly 28. Thebase-frame 22 includes a pair of aligned support platforms 30 and 32 anda pair of cross-members 34. The support platforms 30 and 32 each haveopposed front and rear ends 36 and 38, respectively. The cross-member34A is coupled to the front end 36 of the support platform 30 andextends to the front end of the support platform 32 and is coupledthereto. Similarly, the cross-member 34B is coupled to the rear end 38of each support platform 30 and 32 and extends therebetween.

In one preferred embodiment, the ASA 14 is suspended from arm 18 bysupport cables 17, which are coupled to the cross members 34. Thecontroller 16 positions the ASA 14 above a desired section of theaircraft, and then lowers the ASA 14 onto the desired sections. The ASA14 can be raised or lowered by either moving the arm 18 upward ordownward or by reeling the support cables 17 in or out. Either way, withthe ASA 14 positioned on the skin 6, slack is introduced into the cables17, so that vibrations are not transferred between the arm 18 and ASA14.

In one preferred embodiment, the support platform 30 and 32 and thecross members 34 define a rigid structure having a closed perimeter andan open interior. The open interior extends between the supportplatforms 30 and 32 from the cross member 34A to the cross member 34B. Aprojection of the open interior onto the skin 6 represents a maximumscan area, i.e., the area of the skin 6 that is scanned when thebase-frame 22 is attached to the skin 6. In some situations, the desiredscan area is less than the scan area defined by the base-frame 22.

The base-frame 22 further includes legs 40 that extend from the baseframe 22 outward. Each of the legs 40 includes a suction cup 42 that ispressed onto the skin 6 of aircraft 8 to hold the base frame 22 in placeduring a scan. In one preferred embodiment, when the suction cups 42 arepressed against the skin 6, the footprint of each suction cup 42 doesnot extend into the scanned area. In the preferred embodiment, thesuction cup 42 is adapted for remote actuation so that when the suctioncup 42 contacts the skin 6, the suction cup is activated by a vacuum ora piezoelectric motor to adhere to the skin 6.

Extending between the support platforms 30 and 32 is the moveableplatform 24, which is coupled to the support platforms 30 and 32 suchthat the moveable platform 24 can slide between the front end 36 andrear end 38 of each support platform 30 and 32 respectively.

In one preferred embodiment, each of the support platforms 30 and 32 andthe moveable platform 24 include a linear motor 44 and a table 46.Linear motors are well known to those skilled in the art and will not bediscussed in detail. However, a linear motor 44 includes a magneticstrip 48 and a forcer 50 that slides along the magnetic strip 48responsive to generated electromagnetic fields. Electromagnetic fieldsare used to both move the forcer 50 and to hold the forcer 50stationary. Each one of the tables 46 is attached to a single forcer 50.The table 46 moves in conjunction with the forcer 50. In one preferredembodiment, each table 46 defines a generally flat surface having aplurality of mounting holes (not shown), which can be threaded, formedtherein. For each table 46, the mounting holes of are adapted to receivefasteners such as, but not limited to screws, bolts and other fastenersknown to those skilled in the art so that objects can be attachedthereto. In one preferred embodiment, each table 46 and forcer 50 of alinear motor 44 is integrated into a single unit.

The controller 16 is in communication with each of the linear motors 44via cables 52, which are typically electrical wires or bundles ofelectrical wires. The cables 52 are used for providing electrical powerto the linear motors 44 and for providing a communication link betweenthe controller 16 and the linear motors 44 for, among other thing,communicating positioning information.

Those skilled in the art will recognize that linear motors 44 are merelyone mechanism for slidably coupling the elements of the jig together andthat other mechanisms including but not limited to jackscrews, wormgears, rack and pinion assemblies, and piezoelectric motion control canbe used and are intended to be within the scope of the invention.Typically such mechanisms includes a table or a mounting element thatcontrollably slides along the mechanism by some sort of driving force,such as for example, the rotation of a jackscrew. Thus, the use oflinear motors 44 in the ASA 14 is a matter of design choice and is anon-limiting example.

In one preferred embodiment, the moveable platform 24 is removablyattached to the tables 46A and 46B by fasteners such as screws or bolts(not shown). However, in an alternative embodiment, the moveableplatform 24 is affixed to the tables 46A and 46B by welding or bonding.Those skilled in the art will recognize that welding or bonding are onlytwo methods of affixing and are used here as non-limiting examplesmethods to affix two or more objects.

In one preferred embodiment, the magnetic strips 48A and 48B of thelinear motors 44A and 44B, respectively, extend between the front end 36and rear end 38 of the support platforms 30 and 32, respectively. Thus,the forcers 48A and 48B with tables 46A and 46B attached thereto,respectively, can traverse between the front end 36 and rear end 38 in alongitudinal direction that is defined by the support platform 30.

The moveable platform 24 extends between the aligned support platforms30 and 32 and is attached to the tables 46A and 46B of each supportplatform 30 and 32. Thus, the moveable platform 24 can be longitudinallypositioned anywhere along the magnetic strips 48A and 48B, and itsposition is governed by the controller 16. Initially, the forcers 50Aand 50B of the linear motors 44A and 44B are positioned proximal to thefront end 36 of the support platforms 30 and 32. The controller 16provides positioning signals to the linear motors 44A and 44B of thesupport platforms 30 and 32, respectively, such that the forcers 50A and50B with tables 46A and 46B attached thereto essentially move in unisonand essentially maintain a relative fixed position.

In one preferred embodiment, the moveable platform 24 defines atransverse direction, and the magnetic strip 48C of the moveableplatform 24 is of sufficient length such that it extends along themoveable platform 24 between the support platforms 30 and 32. Thus, thetransverse position of the forcer 50C with table 46C attached theretocan be positioned by the controller 16 anywhere between the supportplatforms 30 and 32 along the moveable platform 24.

The acoustic transducer pivoting assembly 28 is attached to the table46C of the moveable platform 24 by a generally L-shaped mountingplatform 80. The mounting platform 80 includes a first arm 82 that ismounted to the table 46C and a second arm 84 that extends approximatelyperpendicularly from the first arm 82. The first arm 82 is mounted tothe table 46C such that the second arm 84 is aligned approximatelyparallel to the transverse direction defined by the moveable platform24.

In one preferred embodiment, the first arm 82 is of sufficient lengththat the second arm 84 overhangs a side of the moveable platform 24.However, in an alternative preferred embodiment, the second arm 84extends generally upward from the first arm 82, and the first arm 82 isof sufficient length such that the acoustic transducer pivoting assembly28 can couple to the second arm 84 without touching the moveableplatform 24.

In one preferred embodiment, each of the arms 82 and 84 define aplurality of mounting holes (not shown) for receiving fasteners such as,but not limited to, screws and bolts. The mounting platform 80 isremovably attached to the table 46C by fasteners (not shown), whichextend though the mounting holes in the first arm 82 and couple with themounting holes defined table 46C. In one preferred embodiment, the firstarm 82 is fixedly attached to the table 46C. The mounting holes definedby the second arm 84 are adapted to receive fasteners (not shown) forcoupling with the acoustic transducer positioning assembly 28.

Referring to FIG. 2A, the acoustic transducer positioning assembly 28includes a moveable arm 26, an acoustic transducer assembly 54, androtary devices 56 and 58. The rotary devices 56 and 58 operateindependently so that the acoustic transducer assembly 54 can be rotatedabout two axes, and the moveable arm is aligned approximatelyvertically. The moveable arm 26, the rotary devices 56 and 58 areconfigured to provide a total of 5 degrees of freedom, longitude,transverse, vertical, and two rotational degrees of freedom, pitch andyaw, for the acoustic transducer assembly 54.

In one preferred embodiment, the moveable arm 26 includes a linear motor44D having a magnetic strip 48D and a forcer 50D with a table 48Dattached thereto. The linear motor 44D is merely one mechanism forproviding the acoustic transducer assembly 54 with a vertical degree offreedom and that the other mechanisms including but not limited tojackscrews, worm gears, rack and pinion assemblies, and piezoelectricmotion control can be used and are intended to be within the scope ofthe invention.

The moveable arm 26, the rotary devices 56 and 58, and the acoustictransducer assembly 54 are in communication with the controller 16 viacables 52. Commands from the controller 16 and electrical power aresupplied to the moveable arm 26 and the rotary devices 56 and 58 throughcables 52. The acoustic transducer assembly 54 receives signals from thecontroller 16, which causes the acoustic transducer assembly 54 to pingthe skin surface of the aircraft 8, i.e., to emit an acoustic signalthat impinges upon the skin 6. The acoustic transducer assembly 54 sendsan echo identical signal to the controller 16. The echo signalcorresponds to acoustical signals received by the acoustic transducerassembly 54 that are reflections of the ping.

Rotary devices are well known in the art and shall not be discussed indetail. A non-limiting example of a rotary device is a direct driverotary table by Parker model no. DM1004.

In one embodiment, the moveable arm 26 is attached to the second arm 82of the mounting platform 80 by fasteners (not shown) and is aligned suchthat the moveable arm 26 defines an axis that is approximatelyperpendicular to both the longitudinal direction and the transversedirection. The magnetic strip 48D extends in the direction of the axisalong the moveable arm 26. Thus, the forcer 50D with table 46D attachedthereto is positionable by the controller 16 in the direction of theaxis along the moveable arm 26.

In one preferred embodiment, the rotary device 56 includes opposed mount60 and table 62. The mount 60 defines a generally flat surface, which ismounted to the table 46D by fasteners such as screws or bolts. The table62 defines a generally flat mounting surface, which is approximatelyparallel to the mount 60. The mount 60 and table 62 are pivotallycoupled together such that the generally flat mounting surface definedby the table 62 is approximately perpendicular to the axis of rotation,which is called the pitch axis. The table 62 includes a plurality ofmounting holes (not shown), which can be threaded and which are adaptedto receive fasteners such as, but not limited to, screws or bolts foraffixing objects thereto.

An L-shaped mounting plate 64 is mounted to the table 62 by fastenerssuch as screws or bolts. The L-shaped mounting plate 64 includes a firstarm 66, which is attached to the table 62, and a second arm 68, which isaligned approximately perpendicular to the first arm 66. The second arm68 includes a plurality of mounting holes (not shown) for receivingfasteners such as screws and bolts for affixing objects thereto. Therotary device 58 is attached to the second arm by fasteners and issubstantially similar to the rotary device 56.

The rotary device 58 includes a mount 70, which defines a first flatsurface, and a table 72, which defines a second flat surface that issubstantially parallel to the first flat surface. The mount 70 isattached to the second arm 68 by fasteners and the table 72 is pivotallycoupled to the mount 70.

The table 72 includes a plurality of mounting holes (not shown) whichcan be threaded for receiving fasteners. The table 72 is pivotableamount a yaw axis that is approximately perpendicular to the generallyflat surface defined by the table 72.

In one embodiment, the acoustic transducer assembly 54 is cylindricaland has a threaded end 74 and an opposed end 76, where acoustic signalsare emitted and received. The threaded end 74 is removably attached to amounting block 78 by screwing the threaded end 74 into a threaded hole(not shown) formed in mounting block 78. The mounting block 78 isremovably attached to table 72 by fasteners such as screws or bolts.

Acoustic signals emitted from the acoustic transducer assembly 54 have apredetermined focal length and by adjusting the position of table 46(d)along moveable arm 26 and adjusting the alignment of the acoustictransducer assembly 54 using rotatable devices 56 and 58 the emittedacoustic signals can be focused above, on, or below the surface of theskin 6 such that the propagation direction of the emitted acousticsignal is normal to the surface or non-normal to the surface.

The controller 16 can move the acoustic transducer pivoting assembly 28in two dimensions: along the longitudinal direction by moving theforcers 50A and 50B; along the transverse direction by moving the forcer50C. Furthermore, the controller 16 can move the acoustic transducerassembly 54 along the axis defined by moveable arm 26 by moving theforcer 50D of linear motor 44D and rotate the acoustic transducerassembly about two axes the pitch and yaw axes, using rotatable devices56 and 58. Because the acoustic transducer assembly 54 has five degreesof freedom, the controller 16 can position the acoustic transducerassembly 54 so as to compensate for the contour of the scanned skin 6during a scan of the skin 6 of the aircraft 8. In other words, thevertical distance between the acoustic transducer assembly 54 and theskin 6 can be held constant or changed during a scan, regardless ofwhether the scanned skin 6 is flat or curved or irregular, and theacoustic transducer assembly 54 aligned perpendicular ornon-perpendicularly to the skin 6.

In an alternative embodiment, the elements of the acoustic transducerpivoting assembly 28 is configured in the manner illustrated in FIG. 10.The rotary device 56 is coupled to the mounting platform 80 (not shown),which is coupled to the table 46C (not shown) of the moveable platform24. The rotary device 56 is aligned approximately vertically, and theL-shaped mounting plate 64 is attached to the table 62 of the rotarydevice 56. The rotary device 58 is mounted to the second arm 68 of theL-shaped mounting platform 64 in the manner previously described.Attached to the table 72 of the rotary device 58 is the moveable arm 26.Thus, the moveable arm 26 has two degrees of freedom and can be rotatedabout the pitch axis by rotation of table 56 and about the yaw axis byrotation of table 72. The acoustic transducer assembly 54 is coupled tothe table 46D, which is coupled to the forcer 50D, and can be movedalong the axis defined by the moveable arm 26. Thus, in thisconfiguration, the acoustic transducer assembly 54 still has fivedegrees of freedom.

Referring to FIG. 3, in an alternative, the ASA 14 includes a housing304 that is attached to the cross member 34B. Typically, the housing 304is water resistant so as to protect internal components and includes anamplifier (not shown): The amplifier is in communication with thecontroller 16 via cable 52B and with the acoustic transducer assembly 54via cable 52A. The amplifier receives the echo electrical signal fromthe acoustic transducer assembly 54 and amplifies it, and transmits theamplified signal to the controller 16 via cable 52B. Amplifying thesignal from the acoustic transducer assembly 54 enables the operator toincrease the distance between the acoustic transducer assembly 54 andthe controller 16 or devices that receive and store or analyze thesignal.

In another preferred embodiment, the housing includes a storage device(not shown), the storage device stores the received echo electricalsignals from the acoustic transducer assembly 54. The stored echosignals can be download during a scan or at the end of the scan.

Conceptually a scan is performed on the a scan segment 300 of the skin 6by associating sub-areas 302 of the scan segment 300 with scan points.The dashed lines 304 and the base-frame 22 define each of the sub-areas302. At the beginning of a scan, the acoustic transducer pivotingassembly 28 is positioned by the controller 16 so that the acoustictransducer assembly 54 is approximately centered on the first scan pointlabeled (x₁, y₁). The acoustic transducer assembly 54 emits an acousticsignal that pings or impinges on the sub-area 302 associated with thescan point (x₁, y₁). The acoustic transducer assembly 54 then receivesacoustic signals that the are reflections of the emitted acousticsignal. The acoustic transducer assembly 54 converts the reflectedacoustic signals into electrical signals, and transmits the electricalsignals to the amplifier, which in turn amplifies and transmits thesignal to the controller 16.

In response to commands from the controller 16, the acoustic transducerpivoting assembly 28 is moved by an amount of delta x in the transversedirection, and then the acoustic transducer assembly 54 repeats theprocess of emitting an acoustic signal and receiving reflected acousticsignals. Typically, a transverse scan segment is completed after all ofthe scan points that have the same longitudinal value, i.e., the same yvalue, between x₁ and x_(m), inclusive, have been scanned. However, insome situations, the operator may choose to have a transverse scan thatis merely a portion of the scan points having the same longitudinalvalue between the support platforms 30 and 32. In that case, thecontroller 16 scans the acoustic transducer over the selected scanpoints.

Once a transverse scan has been completed, the controller 16 translatesthe forcer 50C with acoustic transducer pivoting assembly 28 coupledthereto such that the acoustic transducer pivoting assembly 28 isrepositioned above the first scan point of that transverse run. Next,the controller 16 translates the moveable support platform 24 by anamount delta y by repositioning the forcers 50A and 50B by the amountdelta y. The controller 16 then commences with another transverse scan.In this manner, all of the scan points from (x₁, y₁) to (x_(m), y_(n)),inclusive, or a sub-portion of the thereof, are scanned. The transversedistance, delta x, and longitudinal distance, delta y, are predeterminedby the operator. Typical, delta x and delta y are in the 20-50 micronrange.

Acoustic Scan

Referring to FIG. 4, at time t₁ the acoustic transducer assembly 54emits an acoustic signal 402A. The acoustic signal 402B acousticallyimpinges the surface of sub-area 302 of the skin 6 at time t₂.Typically, the signals 402A and 402B are the same, however, in somesituations the magnitude of signal 402B is less than the magnitude ofsignal 402A because a portion of signal 402A is reflected, scattered, orabsorbed before it impinges upon the surface of the sub-area 302. Theacoustic signals 402B, 402C, 402D, and 402E are all at least a portionof the emitted acoustic signal 402A. They are designated differently todenote changes in their magnitudes due to reflections and absorption.

The skin 6 is a laminate 404 made up of multiple layers of at least onematerial 406 and adhesive layers 408. Acoustic signals are partiallyreflected at the interface of any discontinuity in the acousticimpedance of the medium through which the acoustic signal is traveling.Discontinuities can be caused by, among other things, stresses withinthe material or by changes in density, which typically occur at theinterface of the adhesive layer 408 and the material layer 406 and atthe surface of the skin 6. Thus, at time t₂ a portion of the acousticsignal 402B penetrates the surface of the sub-area 302 and propagatesinto the laminate 408 and a portion of the signal is reflected backwardstowards the acoustic transducer assembly 54, the reflected portion ofthe signal is the acoustic signal 412.

At time t₃, the acoustic signal 402C is incident upon the interface ofthe adhesive layer 408A and material 406A, where another portion of theemitted signal 402 is reflected. Similarly, at time t₄ some of theacoustic signal 402D is reflected at the interface of the adhesive layer408A and material 406B.

The magnitude of the reflected acoustic signal 412 is related to boththe size of the discontinuity and to the magnitude of the change in theacoustic impedance. A void in a material will generally produce such alarge change in the acoustic impedance of the material that an acousticsignal will be totally reflected. Thus, at time t₅, the acoustic signal402E is essentially totally reflected by the void 410 in adhesive layer408B.

It should be remembered that any change in the acoustic impedance of amedium reflects acoustic signal propagating in that medium.Consequently, the acoustic signal 402 will normally be reflected at boththe interfaces of different layers of material and within one or morelayers of a material. The reflections shown in FIG. 4 are merelyillustrative and are not intended to signify all of the reflections thatoccur within the laminate 404.

Typically, the acoustic transducer assembly 54 emits a single acousticsignal 402 that is incident on the sub-area 302 and receives a series ofreflected acoustic signals 412, where each of the reflected acousticsignals 412 corresponds to a change in the acoustic impedanceencountered by the emitted acoustic signal 402. FIG. 5 is a digitizedrepresentation of the acoustic signals received by the acoustictransducer assembly 54 versus time and is known as an A-Scan. Thedigitized acoustic signal 502 is made up of a series of pulses thatinclude pulse 504, pulse 506 and pulse 508.

The pulse 504 is the first pulse received by the acoustic transducerassembly 54 and corresponds to the portion of the emitted acousticsignal that was reflected from the surface of the sub-area 302, i.e.,the first discontinuity in the acoustic impedance encountered by theacoustic signal 402. The pulses 506 and 508 occurred later in time thanpulse 504, and therefore, they correspond to discontinuities in theacoustic impedance of the laminate 404. Typically, the pulse 504 is usedas a reference pulse, and the time lag between the when the acousticsignal 402A was emitted and when the pulse 504 is received is used for,among other things, determining the distance between surface of thesub-area 302 and the acoustic transducer assembly 54. The relativemagnitude of the reflected pulse 504 with respect to the emitted signal402A can also be used for, among other things, determining whether theacoustic transducer assembly 54 is properly aligned with the surface ofthe sub-area 302.

In one preferred embodiment, the acoustic signal 502 is divided intomultiple time slices such as the time slices shown by gates 510A and510B. In one preferred embodiment, the acoustic signal 502 is dividedinto approximately thirty time slices, which can overlap, or abutadjacent time slices, or be distinct, and the time slices can also havedifferent widths. Each time slice that occurs after pulse 504 measuresacoustic reflections from a layer within the laminate 408. In onepreferred embodiment, the time slices are measured relative to pulse 504rather than from when the acoustic signal 402A was emitted from theacoustic transducer assembly 54. By using the pulse 504 as a referencepoint, a time slice corresponds to a layer of material at a given depthfrom the surface of the material. Whereas, when the time slice ismeasured from the time the signal was emitted from the acoustictransducer, a time slice corresponds to a layer at a given distance fromthe acoustic transducer. Therefore, using the pulse 504 as the referencepoint, one can scan the acoustic transducer assembly 54 across thesurface of the skin 6 at different heights from the surface and stillmeasure the acoustic characteristics for a layer at constant depth fromthe surface.

In FIG. 6 an image of a layer of a scanned laminate is shown, and theimage is known as a C-Scan. In this image the scan points areapproximately 20-50 microns apart, and each point of the imagecorresponds to a digitized representation of the amplitude of areflected acoustic signal 502 within a predetermined time slice 510. Thedark regions represent regions where the amplitude of the reflectedsignal was low and the light regions represent larger amplitudes of thereflected signal. The points labeled 602 are rivets that extend throughthe laminate. The points labeled 604 are voids in the adhesive layer.

Controller

Referring to FIG. 7, in one preferred embodiment, the controller 16 is ageneral purpose digital computer, such as a personal computer (PC;IBM-compatible, Apple-compatible, or otherwise), workstation,minicomputer, or mainframe computer. Generally, in terms of hardwarearchitecture, as shown in FIG. 8, the computer 16 includes a processor702, memory 704, one or more input and/or output (I/O) devices 706 (orperipherals) that are communicatively coupled via a local interface 708,and a signal analyzer 718 that receives the reflected acoustic signals502 from the acoustic transducer assembly 54 for each scan point. Thelocal interface 708 can be, for example but not limited to, one or morebuses or other wired or wireless connections, as is known in the art.The local interface 708 may have additional elements, which are omittedfor simplicity, such as controllers, buffers (caches), drivers,repeaters, and receivers, to enable communications. Further, the localinterface may include address, control, and/or data connections toenable appropriate communications among the aforementioned components.

The processor 702 is a hardware device for executing software,particularly that stored in memory 704. The processor 702 can be anycustom made or commercially available processor, a central processingunit (CPU), an auxiliary processor among several processors associatedwith the computer 16, a semiconductor based microprocessor (in the formof a microchip or chip set), a macroprocessor, or generally any devicefor executing software instructions. Examples of suitable commerciallyavailable microprocessors are as follows: a PA-RISC seriesmicroprocessor from Hewlett-Packard Company, an 80×86 or Pentium seriesmicroprocessor from Intel Corporation, a PowerPC microprocessor fromIBM, a Sparc microprocessor from Sun Microsystems, Inc, or a 68xxxseries microprocessor from Motorola Corporation.

The memory 704 can include any one or combination of volatile memoryelements (e.g., random access memory (RAM, such as DRAM, SRAM, SDRAM,etc.)) and nonvolatile memory elements (e.g., ROM, hard drive, tape,CDROM, etc.). Moreover, the memory 704 may incorporate electronic,magnetic, optical, and/or other types of storage media such as R-CD andR-DVD. Note that the memory 704 can have a distributed architecture,where various components are situated remote from one another, but canbe accessed by the processor 702.

Information relating to the reflected acoustic signal 412 is stored inmemory 704. The related information includes reflected acoustic signal412 such as the digitized acoustic signal 502 and a position indicatorthat associates the acoustic signal 502 with a scan point. Frequently,the digitized acoustic signal 502 is stored for only selected scanpoints instead of for every scan point. The related information alsoincludes digitized times slices that are associated with scan points,which are used for, among other things, generating images of layers suchas the image of FIG. 6. The related information can also includetransforms of temporal or spatial data associated with acoustic signals502. For example, the acoustic signal 502 is temporal function that canbe transformed into a frequency spectrum by a Fourier-Transform, and inthat case, the frequency spectrum is stored in memory 704.

The software in memory 704 may include one or more separate programs,each of which comprises an ordered listing of executable instructionsfor implementing logical functions. In the example of FIG. 7, thesoftware in the memory 704 includes the Application logic 710 inaccordance with the present invention and a suitable operating system(O/S) 712. A non-exhaustive list of examples of suitable commerciallyavailable operating systems 712 is as follows: (a) a Windows operatingsystem available from Microsoft Corporation; (b) a Netware operatingsystem available from Novell, Inc.; (c) a Macintosh operating systemavailable from Apple Computer, Inc.; (d) a UNIX operating system, whichis available for purchase from many vendors, such as the Hewlett-PackardCompany, Sun Microsystems, Inc., and AT&T Corporation; (e) a LINUXoperating system, which is freeware that is readily available on theInternet; (f) a run time Vxworks operating system from WindRiverSystems, Inc.; or (g) an appliance-based operating system, such as thatimplemented in handheld computers or personal data assistants (PDAs)(e.g., PalmOS available from Palm Computing, Inc., and Windows CEavailable from Microsoft Corporation). The operating system 712essentially controls the execution of other computer programs, such asthe Application logic 710, and provides scheduling, input-outputcontrol, file and data management, memory management, and communicationcontrol and related services.

The Application logic 710 includes one or more source programs,executable programs (object codes), scripts, or any other entitiescomprising a set of instructions to be performed. A source program istranslated via a compiler, assembler, interpreter, or the like, whichmay or may not be included within the memory 704, so as to operateproperly in connection with the O/S 712. Furthermore, the Applicationlogic 710 can be written as:

-   (a) an object oriented programming language, which has classes of    data and methods, or-   (b) a procedure programming language, which has routines,    subroutines, and/or functions, for example but not limited to, C,    C++, Pascal, Basic, Fortran, Cobol, Perl, Java, and Ada. In one    preferred embodiment, the Application logic 710 includes positioning    logic 714 and scan logic 716.

The processor 702 uses the positioning logic 714 to control the positionand alignment of the acoustic transducer assembly 54. Specifically, theprocessor 702 sends positioning/alignment commands to the linear motors44 of the support platforms 30 and 32, moveable platform 24, moveablearm 26, and the rotational devices 56 and 58. The processor 702 alsoimplements the scan logic 716 to send the acoustic transducer assembly54 signal commands that cause the acoustic transducer assembly 54 toemit acoustic signals. In one embodiment, the scan logic also includelogic for generating a digitized image of a scan area, such as the imageshown in FIG. 6, and logic for analyzing data such as, but not limitedto, Fourier-Transform logic.

The I/O devices 706 may include input devices, for example but notlimited to, a keyboard, mouse, scanner, microphone, etc. Furthermore,the I/O devices 706 may also include output devices, for example but notlimited to, a printer, display, etc. Finally, the I/O devices 706 mayfurther include devices that communicate both inputs and outputs, forinstance but not limited to, a modulator/demodulator (modem; foraccessing another device, system, or network), a radio frequency (RF) orother transceiver, a telephonic interface, a bridge, a router, etc. TheI/O devices 706 include devices that are coupled to the linear motors44A-44D, the rotational devices 56 and 58, and the acoustic transducerassembly 54 via communication cables 52.

If the computer 16 is a PC, workstation, or the like, the software inthe memory 704 may further include a basic input output system (BIOS)(omitted for simplicity). The BIOS is a set of essential softwareroutines that initialize and test hardware at startup, start the O/S712, and support the transfer of data among the hardware devices. TheBIOS is stored in ROM so that the BIOS can be executed when the computer16 is activated.

When the computer 16 is in operation, the processor 702 is configured toexecute software stored within the memory 704, to communicate data toand from the memory 704, and to generally control operations of thecomputer 16 pursuant to the software. It should be noted that theApplication logic 710 can be stored on any computer readable medium foruse by or in connection with any computer related system or method. Inthe context of this document, a computer readable medium is anelectronic, magnetic, optical, or other physical device or means thatcan contain or store a computer program for use by or in connection witha computer related system or method. The Application logic 710 can beembodied in any computer-readable medium for use by or in connectionwith an instruction execution system, apparatus, or device, such as acomputer-based system, processor-containing system, or other system thatcan fetch the instructions from the instruction execution system,apparatus, or device and execute the instructions. In the context ofthis document, a “computer-readable medium” can be any means that canstore, communicate, propagate, or transport the program for use by or inconnection with the instruction execution system, apparatus, or device.The computer readable medium can be, for example but not limited to, anelectronic, magnetic, optical, electromagnetic, infrared, orsemiconductor system, apparatus, device, or propagation medium. Morespecific examples (a non-exhaustive list) of the computer-readablemedium would include the following: an electrical connection(electronic) having one or more wires, a portable computer diskette(magnetic), a random access memory (RAM) (electronic), a read-onlymemory (ROM) (electronic), an erasable programmable read-only memory(EPROM, EEPROM, or Flash memory) (electronic), an optical fiber(optical), and a portable compact disc read-only memory (CDROM)(optical). Note, the computer-readable medium could even be paper oranother suitable medium upon which the program is printed. As theprogram can be electronically captured, via for instance opticalscanning of the paper or other medium, then compiled, interpreted orotherwise processed in a suitable manner if necessary, and then storedin a computer memory.

In an alternative embodiment, where the Application logic 710 isimplemented in hardware, the Application logic 710 can implemented withany or a combination of the following technologies, which are each wellknown in the art: a discrete logic circuit(s) having logic gates forimplementing logic functions upon data signals, an application specificintegrated circuit (ASIC) having appropriate combinational logic gates,a programmable gate array(s) (PGA), a field programmable gate array(FPGA), etc. In addition, the scope of the present invention includesembodying the functionality of the preferred embodiments of the presentinvention in logic embodied in hardware or software-configured mediums.

In one embodiment, the positioning logic 714 uses a portion of theacoustic signal 502 for determining the current position and alignmentor subsequent positions and alignments of the acoustic transducerassembly 54. For example, using reflected signals 502 from previous scanpoints, the positioning logic 714 can determine the desired vertical androtational position of the acoustic transducer assembly 54 at itscurrent scan point. By calculating the rate of change of the verticalposition and rotational alignment of the acoustic transducer assembly 54from previous scan points and predicting the vertical position androtational alignment of the acoustic transducer assembly 54 at itscurrent position. In another embodiment, the desired vertical androtational position of the acoustic transducer assembly 54 aredetermined by using feedback. In this embodiment, the acoustictransducer assembly 54 emits a first acoustic signal and based upon thereflected acoustic signal 502 and the positioning logic 714, theprocessor 702 determines whether the current vertical position andcurrent rotational position of the acoustic transducer assembly 54 arecorrect. If the acoustic transducer assembly 54 is not correctlypositioned and aligned, the processor 702 sends newpositioning/alignment commands and rescans the current point. Theprocessor 702 continues to correct the position and alignment of theacoustic transducer assembly 54 until some or all of the receivedreflected signal 502 falls within some predetermined parameter range, atwhich point, the received signal 502 is used for analysis.

In one embodiment, the signal analyzer 718 is hardware configured toanalyze signals from the acoustic transducer assembly 54, which arereceived at the computer via I/O device 706. The signal analyzer 718 istypically an analog-to-digital converter (ADC) that is adapted to have asample rate that may be in the giga-Hertz range.

In one preferred embodiment, the time slices, which were shown in FIG.6, are wide enough for the signal analyzer 718 to sample 20 to 30 pointswithin each time slice. The output from the signal analyzer 718 for eachtime slice is then the magnitude of the largest sample point. In oneembodiment, the output also includes the phase of the largest sampledpoint. The output from each time slice is then stored in memory 704 andis associated with the current longitudinal and transverse position ofthe acoustic transducer assembly 54.

In one embodiment, the computer 16 also includes a signal processor 820that is used for, among other things, Fourier-Transforms of the receivedreflected signal 502. Thus, the received acoustic signal 502 istransformed from a temporal quantity to a frequency spectrum. Thefrequency spectrum is associated with the current longitudinal andtransverse location of the acoustic transducer assembly 54 and stored inmemory 704. The signal processor 720 is typically hardware such as anASIC, FPGA, or DSP.

Those skilled in the art will recognize that implementing the signalanalyzer 718 and the signal processor 720 in hardware is a designchoice. In alternative embodiments, either the signal analyzer 718 orthe signal processor 720 or both of them are implemented in eithersoftware or firmware.

In one preferred embodiment, the digitized reflected signals of eachtime slice and the frequency spectrums of the reflected signals 502 arerecorded on a media such as a CD or DVD. The recorded scan becomes asnap shot in time of the internal structure of the scanned area. In thefuture, another scan can be compared with the current scan to determinehow, or whether, the internal structure has changed.

Referring to FIG. 8, in an alternative embodiment, the controller 16includes a computer 802, a motor control unit (MCU) 804 and apulser/receiver unit 806. In this embodiment, the computer 802 receives,processes, and stores data, and among other things, synchronizes themovement of the acoustic transducer assembly 54 with the emission ofacoustic signals 402. The motor control unit 804 is in communicationwith the computer 802 via the communication link 808 and with the linearmotors 44 of ASA 14 via the cables 52. Motor control units are wellknown in the art and shall not be described in detail. An example of amotor control unit is a Parker Automation Model GEM6K drive/controller.

In one preferred embodiment, the motor control unit 804 is adapted toreceive instructions from the computer 802 and control the position andalignment of the acoustic transducer assembly 54 responsive to theinstructions from the computer 802. Then, the motor control unit 804 isadapted to control the position and alignment of the acoustic transducerassembly 54 using timing signals from the computer 802 and surfaceinformation stored in the motor control unit 802. Typically, thecomputer 802 controls the position and alignment of the acoustictransducer assembly 54 during initialization, and thereafter the motorcontrol unit 804 controls the position and alignment of the acoustictransducer assembly 54 in responsive to move commands from the computer802. When the MCU 804 is controlling the position and alignment of theacoustic transducer assembly 54, the MCU 804 tells the computer 802 thecurrent position of the acoustic transducer assembly 54 after each move.

The pulser/receiver 806 is in communication with the computer 802 viacommunication link 912 and with the acoustic transducer assembly 54 viacables 52. When the acoustic transducer assembly 54 is properlypositioned and aligned, the computer 802 sends a signal to thepulser/receiver 806 via communication link 912. The pulser/receiver 806generates a high voltage signal that is sent to the acoustic transducerassembly 54 via cable 52, which causes the acoustic transducer assembly54 to emit an acoustic signal 412. The acoustic transducer assembly 54sends an electrical signal, or an echo signal that corresponds to thereflected acoustic signal 412 to the pulser/receiver 806 via cable 52.The pulser/receiver 806 then relays the echo signal to the computer 802via communication link 912.

The computer 802 correlates the position of the acoustic transducerassembly 54 with the received echo signal from the pulser/receiver 806.In this embodiment, the computer 802 synchronizes the MCU 804 and thepulser/receiver 806. The MCU 804 moves the acoustic transducer assembly54, and the pulser/receiver causes it to ping. After the acoustictransducer assembly 54 is correctly positioned and aligned by the MCU804, the computer 802 sends a signal to the pulser/receiver 806 thatcauses the acoustic transducer assembly 54 to ping the aircraft 8 byemitting the acoustic signal 402. The MCU 804 does not reposition orrealign the acoustic transducer assembly 54 until the MCU 804 receives amove signal from the computer 802. The computer 802 does not send a movesignal to the MCU 804 until after the computer 802 has received the echosignal from the pulser/receiver 806.

Referring to FIG. 9, which illustrates one method of initializing theASA 14, in step 902, the ASA 14 is positioned on the skin 6 at aposition that is approximately the desired location of the ASA 14. Instep 904, the computer 802 sends a signal to the pulser/receiver 806,which in turn sends a high voltage signal to the acoustic transducerassembly 54 that causes the acoustic transducer assembly 54 to emit theacoustic signal 402, or to “ping” the surface.

In step 906, the acoustic transducer assembly 54 receives the reflectedacoustic signal 412 and thereby produces an electrical signal, or theecho signal that corresponds to the reflected acoustic signal 412. Theecho signal is sent to the computer 802 via the pulser/receiver 808.

In step 908, the computer 802 analyzes the echo signal. In oneembodiment, the echo signal is analyzed to determine the amount ofreflection for a time slice that corresponds to the interface of anadhesive-material layer. If the amount of reflection is smaller than apredetermined threshold, then the computer 802 determines that theacoustic impedance at that layer is substantially uniform, which occurswhen a rivet extends through the adhesive-material interface.

Next, in step 910, the computer 802 determines if the acoustictransducer assembly 54 pinged a known location. The computer 802 knowsthe structural features and the contours of the skin 6 of the aircraftand knows how the structural features such as rivets and contours willreflect acoustic signals. If the echo signal did not correspond to asignal reflected from a known location, then the computer proceeds tostep 912 and has the motor control unit 804 move the acoustic transducerassembly by an amount that is determined by the computer 802. Thecomputer 802 keeps repeating the steps 904 through 912 until theacoustic transducer assembly 54 has pinged a known location.

After the acoustic transducer assembly 54 is positioned above a knownlocation, the computer 802 proceeds to step 914 and initiates the autoscan mode. In auto-scan mode, the motor control unit 804 uses itsknowledge of the contours of the skin 6 to position and align theacoustic transducer assembly 54. In this mode, the computer 802 sendssynchronization signals to the motor control unit 804 andpulser/receiver 806, but the computer 802 no longer need determine theposition and alignment of the acoustic transducer assembly 54.Typically, the MCU 804 and the computer 802 include storage units (notshown) for storing, among other things, structural information, contourinformation, etc. about the aircraft 8. This information is typicallyformatted as a Computer Assisted Design (CAD) file. The MCU 804 uses theCAD file for controlling the position and alignment of the acoustictransducer assembly 54.

Acoustic Coupling

Typically, the acoustic transducer assembly 54 emits an acousticalsignal in the 1-200 Mz frequency range. For example, acoustictransducers such as a Sonix series nos. V313 or MSIC, operate in the1-200 MHz frequency range. A problem associated with operating in thisfrequency range is that air does not readily transmit acoustic signalsin that frequency range because in that frequency range the acousticimpedance of air is so high that acoustic signals are essentiallytotally reflected. In this section, four different preferred embodimentsof devices that enable an operator to perform reflection mode scanningacoustic microscopy of an object such as, but not limited to, theaircraft 8, are described.

Acoustic Transducer Assembly-Solid Acoustic Coupler

In FIG. 10, an acoustic transducer assembly-solid acoustic coupler 1000is shown mounted to the acoustic transducer pivoting assembly 28. Theacoustic transducer assembly-solid acoustic coupler 1000 includes theacoustic transducer assembly 54 and a solid acoustic coupler 1002.

In one preferred embodiment, the solid acoustic coupler 1002 is madefrom a material such as, but not limited to, epoxy, polyimide, resin,ceramic, metal and other materials known to those skilled in the artthat can effectively carry acoustic signals in the 1-200 MHz frequencyrange, or materials that have an acoustic impedance less than air inthat frequency range.

The acoustic transducer assembly 54 emits and receives acousticalsignals from end 76. Typically, the end 76 is open ended and is formedsuch that the end includes a bowl shaped face or a concave face 1004 andthe acoustic transducer assembly 54 emits and receives acousticalsignals through face 1004. Acoustic signals emitted from the acoustictransducer assembly 54 are focused at a predetermined focal length fromthe end 76, typically in the range of 0.25 inches. The focal length ofthe acoustic transducer assembly 54 is determined in part by the shapeof the face 1004.

The solid acoustic coupler 1002 includes opposed ends 1006 and 1008. Theend 1006 is formed such that its shape compliments the shape of face1004 so that end 1006 and face 1004 fit together with little or no gapstherebetween. The longitudinal length of the solid acoustic coupler1002, which is the distance between the opposing ends 1006 and 1008, isapproximately the focal length of acoustic transducer assembly 54. Thus,emitted acoustic signals from the acoustic transducer assembly 54 arefocused at end 1008. However, the longitudinal length of the solidacoustic coupler 1002 is a matter of implementation, and in anotheralternative embodiment, the longitudinal length of the solid acousticcoupler 1002 is less than the focal length of the acoustic transducerassembly 54. In yet another embodiment, the longitudinal length of thesolid acoustic coupler 1002 is greater than the focal length of theacoustic transducer assembly 54.

To scan an object 1010 with the acoustic transducer assembly-solidacoustic coupler 1000, the acoustic transducer pivoting assembly 28 ispositioned such that end 1008 makes physical contact with the surface atpoint 1012. The acoustic transducer assembly 54 emits an acousticsignal, which is carried by the solid acoustic coupler 1002 to thecontact point 1012. Through contact point 1012 and end 1008, acousticsignals are passed between the object 1010 and the solid acousticcoupler 1002. Thus, the solid acoustic coupler 1002 carries emittedacoustic signals, which ping contact point 1012, from the acoustictransducer assembly 54. Pinging contact point 1012 generates acousticsignals, which are reflections of the emitted acoustic signals in object1010. The solid acoustic coupler 1002 carries the reflections to theacoustic transducer assembly 54. After the reflections have beenreceived by the acoustic transducer assembly 54, the controller 16 movesthe acoustic transducer pivoting assembly 28 to a new contact pointwhere the scan process is repeated.

In one embodiment, the acoustic transducer assembly-solid acousticcoupler 1000 is moved between contact points 1012 with the end 1008being generally in contact with the object 1010 during the movementthereof. In this case, the solid acoustic coupler 1002 is preferablymade from a material such as polyimide or other material that will notusually scratch or mar the object 1010.

In another embodiment, when the acoustic transducer pivoting assembly 28is moved between contact points 1012, the acoustic transducer pivotingassembly 28 is first moved away from the object 1010 so that the end1008 is not in contact with the object 1010. Then, the acoustictransducer pivoting assembly 28 is moved to a new position and movedcloser to the object 1010 until the end 1008 reestablishes contact withthe object 1010. In another embodiment, the acoustic transducer pivotingassembly 28 is moved in a saw tooth pattern. In yet another embodiment,one or both of the rotary drives 56 or 58 rotate the acoustic transducerassembly-solid acoustic coupler 1000 such that the end 1008 is not incontact with the object 1010 during movements between contact points1012. After the acoustic transducer pivoting assembly 28 has been movedto a new position, the acoustic transducer assembly-solid acousticcoupler 1000 is then rotated such that the end 1008 reestablishescontact with object 1010.

In one preferred embodiment, the acoustic transducer assembly 54 and thesolid acoustic coupler 1002 are joined together so that there areessentially no gaps between the face 1004 and end 1006. One preferredmethod for accomplishing this is described hereinbelow. The acoustictransducer assembly 54 is positioned such that the acoustic transducerassembly 54 is substantially vertically aligned with face 1004 pointingupward. A mold (not shown) is removably attached to end 76 extendingupwardly therefrom. A predetermined amount of a liquid epoxy or othersuitable material known to those skilled in the art is poured into themold. The liquid flows into the mold and covers the face 1004 of theacoustic transducer assembly 54 and adheres thereto. Typically, theamount of liquid poured into the mold is sufficient to substantiallyfill the mold. After the liquid has hardened into a solid material, themold is removed, thereby exposing the solid acoustic coupler 1002. Inone embodiment, the end 1008 is substantially shaped by the mold. Inanother embodiment, the solid acoustic coupler 1002 is processed to formthe shape of end 1008.

Acoustic Transducer Assembly Sprayer

Referring to FIG. 11, an acoustic transducer assembly sprayer 1100includes the acoustic transducer assembly 54 and a sprayer 1102. Theacoustic transducer assembly 54 includes the opposed threaded ends 74and threaded end 1104. The threaded end 74 is received by a threadedhole (not shown) formed in the mounting block 78, which is mounted tothe table 72 of the rotary device 68.

The sprayer 1102 defines a longitudinal body having opposed ends 1106and 1108. Extending partially between the opposed ends 1106 and 1108 isa chamber 1110. The end 1106 defines a threaded opening (not shown) thatextends from the chamber 1110 to end 1106, and the threaded opening isadapted to mate with the threaded end 1104 of the acoustic transducerassembly 54.

The opposed end 1108 defines a second opening 1114 that is generallyaligned with the threaded opening and which is in communication with thechamber 1110. The sprayer 1102 also defines fluid inlet openings 1116 aand 1116 b, which have spouts 1118 a and 1118 b inserted therein. Thespouts 1118 extend from the chamber 1110 outward beyond the exterior ofthe sprayer 1102.

Pressurized fluid hoses 1120 are coupled to the spouts 1118 and fluidflows therethrough into the chamber 1110. Hydraulic pressure pushesfluid in the hoses 1120 into the chamber 1110, and consequently, a fluidstream 1122 is expelled from the chamber 1110 by the hydraulic pressurecarried by the hoses 1120. The fluid stream 1120 extends outward fromend 1108 of the sprayer 1102 and impinges upon the surface 1124. In onepreferred embodiment, the fluid stream 1122 is a laminar fluid flowstream.

In one preferred embodiment, the fluid inlet opening 1116 a ispositioned such that the spout 1118 a is approximately aimed at theacoustic transducer assembly 54. In this manner, a stream of fluidcarried through tube 1118 flows across the face 1004 of the acoustictransducer assembly 54. Thereby removing any air bubbles from the face.

With the acoustic transducer assembly 54 in communication with the fluidin chamber 1110 and the fluid stream 1122 impinging on the surface 1124,the acoustic transducer assembly 54 is in acoustical communication withthe surface 1124. The acoustic impedance of the fluid is such thatacoustic signals in the 1-200 MHz frequency range are readily carried.Thus, the acoustic transducer assembly-sprayer 1100 is used toacoustically scan an object such as an aircraft, when the aircraft isdisposed in air.

The fluid stream 1122 and the fluid in chamber 1110 communicate acousticsignals between the acoustic transducer assembly 54 and the surface1124. Thus, a scan is performed by having the acoustic transducerassembly 54 emit an acoustic signal that is carried by the fluid inchamber 1110 and the fluid stream 1122 to the surface 1124. The fluidcarries reflections of the emitted acoustic signal back to the acoustictransducer assembly 54. After the acoustic transducer assembly 54 hasreceived the reflection signals, the controller 16 moves the acoustictransducer pivoting assembly 28 to a new position where the process isrepeated. In this manner, an object that is substantially disclosed inair can be scanned with the acoustic transducer assembly-sprayer 1100.

Acoustic Transducer assembly-Fluid Retainer

Referring to FIG. 12, the acoustic transducer pivoting assembly 28 hasan acoustic transducer assembly-fluid retainer 1200 coupled thereto. Inthis embodiment, the acoustic transducer assembly-fluid retainer 1200includes the acoustic transducer assembly 54 and a fluid retainer 1202.The acoustic transducer assembly 54 is coupled to the acoustictransducer pivoting assembly 28 via the mounting block 78 in the mannerpreviously described.

The fluid retainer 1202 defines a longitudinal body having opposed ends1204 and 1206 and the ends 1204 and 1206 each define an opening 1208 and1210, respectively, which are generally vertically aligned. Typically,the longitudinal length of the fluid retainer 1202 is greater than thefocal length of the acoustic transducer assembly 54.

In one preferred embodiment, the opening 1208 is a threaded opening,which is adapted to mate with the threaded end 1104 of acoustictransducer assembly 54. In an alternative embodiment, the acoustictransducer assembly 54 and fluid retainer 1202 are threadably coupledtogether, but the male-female relationship is reversed so that the fluidretainer 1202 screws into end 76 of the acoustic transducer assembly 54.However, in yet another alternative embodiment, the end 1204 of thefluid retainer 1202 is pressure fit onto end 1104 of the acoustictransducer assembly 54 and held thereon by pressure clamps. In yetanother embodiment, the acoustic transducer assembly 54 and fluidretainer 1202 are manufactured as a single non-separable unit.

Extending between opposed ends 1204 and 1206 is a sleeve 1222, which isdefines a fluid retaining chamber 1212. The fluid-retaining chamber 1212is in communication with the openings 1208 and 1210 and contains a fluid1213 therein. The sleeve 1222 is preferably made from a polymer or othernon-rigid material that is essentially impermeable to the fluid 1213.The fluid 1213 carries acoustic signals in the 1 to 200 MHz frequencyrange.

In one preferred embodiment, the end 1204 defines a fluid inlet opening1214 that extends approximately horizontally from the opening 1208thereout, and a spout 1216 having opposed ends 1217 a and 1217 b. Theend 1217 a is aimed at the acoustic transducer assembly 54 so that afluid stream from spout 1216 flows across the face of the acoustictransducer assembly 54. A pressurized fluid hose 1219 is attached to theend 1217 b and a fluid flows therethrough into the fluid retainer 1202.

In one preferred embodiment, the end 1204 also defines a relief valve(not shown). When the end 1206 is in contact with the surface 1218, theend 1206 forms an essentially fluid tight seal on the surface 1218.Thus, when fluid flows into the chamber 1212 through fluid inlet tube1216, air is flushed out of the chamber 1212 through the relief valve.

The end 1206 of the fluid retainer 1202 is annular in shape and is madefrom an resilient pliable material that conforms to the local contour ofa surface 1218 of an object 1220. It is preferable that the end 1206 ismade from a material that is essentially impermeable to the fluid in thefluid retaining chamber 1212.

Encompassing the sleeve 1222 is coil spring 1224 that extends betweenthe opposed ends 1204 and 1206. The coil spring 1224 engages the opposedends 1204 and 1206 and provides a biasing force for pushing the ends1204 and 1206 apart.

The fluid retainer 1202 also includes a pair of overlapping longitudinalsupports 1226 and 1228. The longitudinal support 1226 extends from theend 1204 downward into chamber 1212, and the longitudinal support 1228extends from end 1206 upward into chamber 1212. The longitudinal support1226 and 1228 are approximately cylindrical in shape with thelongitudinal support 1228 having an outer diameter that is smaller thanthe inner diameter of the longitudinal support 1226. Thus, thelongitudinal support 1226 overlaps the longitudinal support 1228 withthe longitudinal support 1228 telescoping within the longitudinalsupport 1226. The longitudinal support 1226 and 1228 are preferably madefrom metal or some other rigid material.

In operation the acoustic pivoting assembly 28 with the acoustictransducer assembly-fluid retainer 1200 attached thereto is positionedsuch that the end 1206 is in contact with the surface 1218. Preferably,the acoustic transducer assembly 54 is brought close enough to thesurface 1218 such that the sleeve 1222 is compressed between ends 1204and 1206. In that case, the coil spring 1224 provides a biasing forcethat pushes the end 1206 against the surface 1218. Typically, the end1206 is pressed against the surface 1218 with sufficient force that itconforms to the local contour of the surface 1218 so as to form anessentially fluid tight seal thereat. However, in one embodiment, thefluid 1213 in the fluid chamber 1212 is under positive pressure from thepressurized fluid hose 1219 so as to prevent air from seeping into thefluid chamber 1212. In that case, some fluid 1213 may seep between theend 1206 and the surface 1218.

The ends 1204 and 1206, the overlapping longitudinal supports 1226 and1228, and the fluid chamber 1212 are aligned so that the acoustictransducer assembly 54 is in acoustic communication with the surface1218 via the fluid 1213. The sleeve 1222, the longitudinal supports 1226and 1228, and the coil spring 1224 cooperate such that the face of theacoustic transducer assembly 54 can be positioned at distance from thesurface 1218 ranging from greater than the focal length of the acoustictransducer assembly 54 to less than the focal length of the acoustictransducer assembly 54. The distance between the face of the acoustictransducer assembly 54 and the surface 1218 can be determined by thecontroller 16 using the time lag between pinging the surface 1218 andreceiving a reflection signal or by using knowledge of the contour ofthe surface 1218 and knowing the position of the acoustic transducerassembly 54.

The longitudinal supports 1226 and 1228 provide longitudinal support tothe sleeve 1222 as the acoustic transducer assembly-fluid retainer 1200is scanned over the surface 1218. When the acoustic transducer assembly54 is moved parallel to the surface 1218, the longitudinal support 1226moves with the acoustic transducer assembly 54 because it and the end1204 are made from rigid materials. As the longitudinal support 1226moves parallel to the surface 1218, it engages the longitudinal support1228 and pushes it in the same direction. The end 1206 moves parallel tothe surface 1218 with the movement of the longitudinal support 1228.Thus, the longitudinal alignment of the food retainer 1202 isessentially maintained as the fluid retainer 1202 is moved across thesurface 1218 even though the sleeve 1222 is pliable and the end 1206 isforming an essentially fluid tight seal on the surface 1218.

Fluid Bath Acoustic Coupler

Referring to FIG. 13, the ASA 14 includes a fluid bath acoustic coupler1300 for coupling acoustic signals between the acoustic transducerassembly 54 and a surface 1302 of an object 1304. The fluid bathacoustic coupler 1300 includes a fluid holder 1306, which is generallypan shaped having an open interior for holding a fluid 1308. The fluidholder 1306 includes a sidewall 1310, which defines the circumference ofthe fluid holder 1306 and which includes an upper portion 1312 and abottom portion 1314, and a top wall 1316 that is attached to the upperportion 1312 of the sidewall 1310.

In this embodiment, the fluid holder 1306 is generally a rectangularshaped pan having right and left sidewalls 1310 a and 1310 b,respectively and a front sidewall (not shown) and a back sidewall 1310c. In other embodiments, the shape of the fluid holder 1306 is differentfrom rectangular and involves fewer or more sidewalls 1310.

The fluid bath acoustic coupler 1300 also includes a brace 1318, whichattaches to the base frame 22 by fasteners 1320, which are typicallyscrews or bolts. Interposing the base frame 22 and the brace 1318 is thesidewall 1310. Thus, the sidewall 1310 is held in place between thebrace 1318 and the base frame 22 by attaching the brace 1318 to the baseframe 22.

The sidewall 1310 is of sufficient length that in operational positionthe sidewall 1306 extends from the upper portion 1312 to the bottomportion 1314 such that the bottom portion 1314 makes contact with thesurface 1302. Typically, the sidewall 1306 is made from a material thatis essentially impermeable to the fluid 1308.

The interior of the fluid holder 1306 is defined by sidewall 1310, whichdefines a closed circumference, and the top wall 1316, which is attachedto the upper portion 1312 of the sidewall 1306 and which essentiallycovers the area enclosed by the sidewall 1316. The top wall 1316 is madefrom a material that is essentially impermeable to the fluid 1308 and ispleated in two dimensions. The top wall 1316 is attached to the sidewall1306 to form an essentially fluid tight seal thereat.

The top wall 1316 defines an opening 1322, which extends through the topwall 1316 and which is in the approximate center of the top wall 1316.The opening 1322 can be moved relative to the right and left sidewalls1310 a and 1310 b, respectively, and relative to the front sidewall (notshown) and the rear sidewall 1310 c because of the two dimensionalpleating in the top wall 1316. The pleats in the top wall 1316 fold andunfold to accommodate the relative movement of the opening 1322.

In one preferred embodiment, the acoustic transducer assembly 54 extendsthrough the opening 1322 such that the face of the acoustic transducerassembly 54 is immersed in the fluid 1308, and the opening 1322 forms anessentially fluid tight seal around the acoustic transducer assembly 54.In one preferred embodiment, a fluid inlet tube 1324, which has aninverted question mark shape is attached to the acoustic transducerassembly 54 such that the hook portion of the question mark isapproximately aimed towards the face (see FIG. 10) of the acoustictransducer assembly 54. The fluid inlet tube 1324 is attached to apressurized fluid hose 1326 and fluid from the hose 1326 flows acrossthe face of the acoustic transducer assembly 54. In one preferredembodiment, the top wall 1316 also includes a relief valve (not shown)through which air escapes from the interior of the fluid holder 1306 asthe fluid holder 1306 is filled with fluid.

The fluid bath acoustic coupler 1300 also includes an interior flap thatextends from the bottom portion 1314 to the sidewall 1310 therein. Theinterior flap 1328 is made from a material such as a polymer, which isessentially impervious to the fluid 1308 and which is conformable to thecontour of the surface 1302. Hydraulic pressure from the fluid 1308essentially holds the interior flap 1328 firmly against the surface 1302to form an essentially fluid type fit around the bottom of the fluidholder 1306.

In one preferred embodiment, the bottom portion 1314 is made from apliable material that conforms to the contour of the surface 1302 of theobject 1304. The bottom portion 1314 also includes a resilient pliablestrip 1330, which is pressed towards the surface 1302 by a plurality ofsprings 1332 that extend from the strip 1330 to the brace 1318. Thus,the bottom portion 1314 is pressed firmly and conformably against thesurface 1302 by the strip 1330, which in turn is biased by the springs1332. With the bottom portion 1314 pressed against the surface 1302, anessentially fluid tight seal is formed between the bottom portion 1314and the surface 1302.

In operation, the acoustic transducer assembly 54 extends throughopening 1322 and is partially immersed in the fluid 1308, whichacoustically couples the acoustic transducer assembly 54 to the area ofthe surface 1302 enclosed by the sidewall 1310. The controller 16 canscan the acoustic transducer assembly 54 over the enclosed area. As theacoustic transducer assembly 54 is scanned over the enclosed area, theacoustic transducer assembly 54 and the opening 1322 move in unison. Inresponse to the movement of the opening 1322, the pleats in the twodimensional pleating of the top wall 1316 fold and unfold to accommodatethe movement of the acoustic transducer assembly 54. In addition, thetwo-dimension pleating of the top wall 1316 accommodate the raising andlowering of the acoustic transducer assembly 54 and pitch and yawrotations by the rotary devices 56 and 58.

In one preferred embodiment, the fluid bath acoustic coupler 1300includes a pair of rollable shutter assemblies 1334 and 1336 thatessentially cover the top wall 1316. The rollable shutter assembly 1334that is attached to the support platforms 30 and 32 above the top wall1316.

The rollable shutter assembly 1334 includes opposed reels 1338 and 1340,which are mounted to the support platforms 30 and 32, respectively, anda shutter 1342. The shutter 1342 is made up of a plurality of slats 1344that extend partially between the cross members 34 a and 34 b, and theslats 1344 are hingedly coupled together. Slats 1344 a and 1344 b areadapted to have a separation distance that is at least the diameter ofthe acoustic transducer assembly 54 so that the acoustic transducerassembly 54 can extend through shutter 1342. When the controller 16moves the acoustic transducer assembly left (right) the acoustictransducer assembly 54 engages slat 1344 a (1344 b) and pushes it in theleft (right) direction, thereby causing reel 1340 (reel 1338) to windand reel 1338 (reel 1340) to unwind shutter 1342.

The rollable shutter assembly 1336 is essentially identical to therollable shutter assembly 1334, and it includes a front reel (notshown), which is mounted to the cross member 34 a, a rear reel 1346,which is mounted to the cross member 34 b, and a shutter 1348 thatextends from the front reel (not shown) to the rear reel 1346. Theshutter 1348 rests upon shutter 1342 and is adapted to slide overshutter 1342.

The shutter 1348 is made up of a plurality of slats, which extendpartially between the support platforms 30 and 32 and which are hingedlycoupled together. As with the rollable shutter assembly 1334, two of theslats are separated by a distance that is at least the diameter of theacoustic transducer assembly 54. Thus, the shutter 1342 defines alongitudinal gap that extends partially between the cross members 34(a)and 34(b), and the shutter 1348 defines a transverse gap extendingpartially between the support platforms 30 and 32.

In operation, the gaps in the rollable shutter assemblies 1334 and 1336and the opening 1322 are aligned so that the acoustic transducerassembly 54 can extend therethrough. When the acoustic transducerassembly 54 is moved forward (backwards) the acoustic transducerassembly 54 engages a slat of the shutter 1348 and pushes the shutter1348 forward (rearward), thereby causing the unseen front reel to wind(unwind) and the rear reel 1346 to unwind (wind) the shutter 1348, whilethe shutter 1342 remains essentially stationary. In one preferredembodiment, the rollable shutter assemblies 1334 and 1336, and the topwall 1316 cooperate such that the acoustic transducer assembly 54 hasfive degrees of freedom.

In one preferred embodiment, the slats of the shutters 1342 and 1348 aremade from a rigid material such as, but not limited to, aluminum. Inthis embodiment, the rollable shutter assemblies 1334 and 1336 areadapted to support the fluid 1308 contained in the fluid holder 1306when the fluid bath acoustic coupler 1300 is inverted. Thus, the ASA 14with the fluid acoustic coupler 1300 attached thereto can be attached toa portion of an object such as the underside of a wing of an aircraftand used for scanning the underside of the wing. In this invertedconfiguration the weight of fluid 1308 is transferred from the fluidholder 1306 and applied to the rollable shutter assemblies 1334 and1336.

Although exemplary preferred embodiments of the present invention havebeen shown and described, it will be apparent to those of ordinary skillin the art that a number of changes, modifications, or alterations tothe invention as described may be made, none of which depart from thespirit of the present invention. Changes, modifications, and alterationsshould therefore be seen as within the scope of the present invention.It should also be emphasized that the above-described embodiments of thepresent invention, particularly, any “preferred embodiments” are merelypossible non-limiting examples of implementations, merely setting fortha clear understanding of the principles of the inventions.

1. An apparatus for examining the internal structure of an object byreflection mode scanning acoustic microscopy, the apparatus comprising:a jig adapted to controllably move an acoustic transducer assembly in atleast two dimensions over a portion of a surface of an object andadapted to removably attach to the object, wherein the object issubstantially disposed in air; a fluid bath for generally containing afluid attached to the jig, the fluid bath having a generally hollowinterior defined by at least one side wall and a top wall, the at leastone side wall defining a closed perimeter and including an upper portionand a bottom portion, the upper portion having the top wall attachedthereto, the top wall substantially covering the interior of the fluidbath and defining a acoustic transducer assembly opening that extendsthrough the top wall, wherein the at least one side wall and the topwall are made from a material that is essentially impermeable to thefluid; and an acoustic transducer assembly having a first end coupled tothe jig and a second end, the second end adapted emit an acoustic signalthat pings a portion of the surface and adapted to receive an acousticsignal that is a reflection of the emitted acoustic signal, wherein theacoustic transducer assembly extends at least partially through theacoustic transducer assembly opening defined by the top wall of thefluid bath such that the second end of the acoustic transducer assemblyis in the interior of the fluid bath.
 2. The apparatus of claim 1,wherein when the jig is attached to the surface of the object, thebottom portion of the at least one side wall conforms to the contour ofthe surface in contact with the bottom portion such that the at leastone side wall forms an essentially fluid tight seal.
 3. The apparatus ofclaim 2, wherein the bottom portion of the at least one side wallincludes a resilient pliable strip for contacting the surface of theobject.
 4. The apparatus of claim 1, further including: an interior flapattached to the bottom portion of the at least one side wall extendingtherefrom into at least a portion of the interior of the fluid bath,wherein the interior flap is made from a material essentiallyimpermeable to the fluid and adapted to conform to the contour of thesurface of the object.
 5. The apparatus of claim 1, further including: abrace attached to the jig with the at least one side wall interposingthe brace and jig; and at least one spring extending from the brace tothe bottom portion of the at least one side wall, wherein the at leastone spring biases the bottom portion of the at least one side wall awayfrom the brace.
 6. The apparatus of claim 1, wherein the jig is adaptedto move the acoustic transducer assembly over the at least a portion ofthe surface of the object enclosed by the at least one side wall, andthe acoustic transducer assembly opening defined by the top wall havingthe acoustic transducer assembly extending therethrough moves inconjunction with the acoustic transducer assembly.
 7. The apparatus ofclaim 6, wherein the top wall is made from a stretchable material thatstretches in response to movement by the acoustic transducer assembly.8. The apparatus of claim 6, wherein the top wall defines multiplepleats that fold and unfold in response to movement by the acoustictransducer assembly.
 9. The apparatus of claim 1, wherein the jigincludes a pair of opposed longitudinal members having first and secondends and defining a longitudinal direction, and a pair of opposed crossmembers defining a transverse direction, one of the cross membersextending between the first ends of the pair of opposed longitudinalmembers, the other cross member extending between the second ends of thepair of opposed longitudinal members, and further including: a firstshutter attached to pair of longitudinal members and extendingtherebetween, wherein the first shutter substantially covers the topwall and defines a longitudinal opening; and a second shutter attachedto pair of cross members and extending therebetween, wherein the secondshutter substantially covers the first shutter and defines a transverseopening, and wherein the longitudinal and transverse openings arealigned with the acoustic transducer assembly opening defined by the topwall such that the acoustic transducer assembly extends through thelongitudinal, transverse and acoustic transducer assembly opening. 10.The apparatus of claim 9, wherein the first shutter is movable in thetransverse direction, and the second shutter is moveable in thelongitudinal direction.
 11. The apparatus of claim 10, wherein when thefluid bath is filled with a fluid and inverted such that the top wall isat the bottom of the fluid bath and the weight of the fluid is appliedto the top wall, the first and second shutters are adapted to supportthe weight of the fluid and the top wall.
 12. The apparatus of claim 1,wherein the jig is adapted to move the acoustic transducer assembly inthree dimensions.
 13. The apparatus of claim 1, wherein the acoustictransducer assembly is coupled to the jig such that the acoustictransducer assembly has at least four degrees of freedom, the at leastfour degrees of freedom including two translational degrees of freedomand two rotational degrees of freedom.
 14. A fluid bath for couplingacoustic signals between an acoustic transducer assembly and an object,wherein the acoustic transducer assembly is used to examine the internalstructure of the object using reflection mode acoustic microscopy, thefluid bath comprising: a top wall; and at least one side wall defining aclosed perimeter and including an upper portion and a bottom portion,the upper portion having the top wall attached thereto, wherein the topwall and the at least one side wall define a body having a generallyhollow interior for containing a fluid, wherein the top wallsubstantially covers the interior and defines an acoustic transducerassembly opening that extends through the top wall, and wherein the atleast one side wall and the top wall are made from a material that isessentially impermeable to the fluid.
 15. The device of claim 14,wherein the fluid bath is adapted to attached to a jig.
 16. The deviceof claim 14, wherein the bottom portion of the at least one side wallincludes a resilient pliable strip for contacting a surface of theobject.
 17. The device of claim 16, further including: an interior flapattached to the bottom portion of the at least one side wall extendingtherefrom into at least a portion of the interior of the fluid bath,wherein the interior flap is made from a material essentiallyimpermeable to the fluid and adapted to conform to the contour of asurface of the object.
 18. The device of claim 14, further including: abrace adapted to attached to the jig with the at least one side wallinterposing the brace and jig; and at least one spring extending fromthe brace to the bottom portion of the at least one side wall, whereinthe at least one spring biases the bottom portion of the at least oneside wall away form the brace.
 19. The device of claim 14, wherein thetop wall defines an area and the acoustic transducer assembly opening ismovable within the area defined by the top wall.
 20. The apparatus ofclaim 19, wherein the top wall is made from a stretchable material. 21.The apparatus of claim 19, wherein the top wall defines multiple pleatsthat fold and unfold in response to movement of the acoustic transducerassembly opening.
 22. A method for examining the internal structure ofan object using reflection mode acoustic scanning microscopy, the methodcomprising the steps of: disposing a fluid bath on a surface of theobject, wherein the fluid bath has a generally hollow interior definedby at least one side wall and a top wall, the at least one side walldefining a closed circumference and having a bottom portion in contactwith a first portion of the surface and enclosing a second portion ofthe surface, the top wall extending from the top portion of the at leastone side wall and substantially covering the second portion of thesurface, wherein the top wall defines an acoustic transducer assemblyopening extending through the top wall, and wherein the object issubstantially immersed in a medium that has a first acoustic impedancefor a given frequency range; disposing an acoustic transducer assemblyhaving first and second ends partially through the acoustic transducerassembly opening defined by the top wall of the fluid bath, wherein thefirst end of the acoustic transducer assembly is adapted to emit andreceive acoustic signals and is located within the interior of the fluidbath; and at least partially filling the fluid bath with a fluid havinga second acoustic impedance, wherein the second acoustic impedance isless than the first acoustic impedance, wherein the fluid extends atleast from the second portion of the surface to the first end of theacoustic transducer assembly; pinging a given area of the second portionof the surface with an acoustic signal emitted from the acoustictransceiver; and receiving reflections of the emitted acoustic signalsat the acoustic transceiver, wherein the emitted signal is reflected bychanges in the acoustic impedance of the object.
 23. The method of claim22, further including the step of: scanning the acoustic transducerassembly over the second portion of the surface, wherein preselectedareas of the second portion of the surface are pinged by the acoustictransducer assembly.
 24. The method of claim 22, wherein the givenfrequency range is approximately 1 to 200 MHz.
 25. The method of claim22, wherein the object is immersed substantially in air.
 26. The methodof claim 22, further including the step of: coupling the acoustictransducer assembly to a jig, wherein the position of the acoustictransducer assembly is governed by the jig.
 27. The method of claim 26,further including the step of: attaching the fluid bath to the acoustictransducer assembly such that movement of the acoustic transducerassembly results in a corresponding movement of the acoustic transducerassembly opening defined by the top wall of the fluid bath.